A lamp with a cool operating temperature in its base region provides several advantages. As used herein, the "base region" of a lamp includes the lamp base and the volume enclosed within the base. Excessive base temperature may adversely affect performance of the lamp. It may shorten the life of the luminaire, the electrical supply circuit, or components of the starter circuit. Excessive base temperature may also result in unsafe heating of combustible materials which form a part of the luminaire or of the materials adjacent to the luminaire. Excessive temperature in the base region may cause failure of the basing cement as well as softening of solder used to connect the lead-in wires to the base.
In modern lamps, it is not uncommon for temperature-sensitive components to be placed in the base region. For example, a high-pressure sodium PAR lamp utilizes a non-linear dielectric element (NLDE) as a component of the starting circuit. The NLDE is situated in the base region. At elevated temperatures, the peak voltage output of the NLDE is reduced. Although heating the NLDE is not a detriment to initial start-up or during lamp operation, it does significantly deter the hot-restart capability of the lamp. This is a serious drawback. Accordingly, adequate thermal isolation of the NLDE during operation is not only desirable but essential for the lamp to be a viable commercial product.
There are various known techniques for reducing the operating temperature of the base region of a lamp. One technique is to increase the distance between the heat source, e.g., arc tube or filament, and the base region. Another technique is to insert insulating material between the heat source and base region. Heat reflective means, such as a metal or mica disk, may be employed to shield the base region from incident radiation. While these techniques are effective, they will generally necessitate increased lamp size or additional materials and associated labor. Moreover, the light-emitting characteristics of the lamp, particularly a PAR lamp, may be comprised by larger lamp size or inclusion of additional materials within the lamp.
It would be an advancement of the art if there were available a method of preventing excessive operating temperatures in the base region of a lamp which does not necessitate increased lamp size nor inclusion of additional insulating or reflective materials within the lamp. Such a method should be simple and inexpensive and, preferably, would involve only slight modification of existing lamp parts.